read(2)/write(2) errno standard for physical devices

[TranKV]

In article <7043 at drutx.ATT.COM>, kvt at drutx.ATT.COM (TranKV) writes:
> To all UNIX/C gurus out there:
> 
> When using read(2)/write(2) to access a physical device in raw mode
> (9-track tape devices specifically), are there a standard errno's that 
> read(2)/write(2) returns to signify end of physical tapes? Or do they 
> vary among UNIX versions and tape drives? If they are indeed different,
> what one can do in application programs to make them portable when
> changing tape drives or machines? All suggestions are appreciated.
> 
> Kim Tran
> AT&T EUO
> 

To add more spices to the discussion, I should have thrown in some
evidences in the first posting. Here they are:

    - Using our 3B5 with UNIX V 2.0, we got errno=5 for both end of
      tape read(2) and write(2).

    - Using our 3B2/600 with UNIX V 3.1 with 9-track tape drive hooked
      up through SCSI, we got errno=28 for end of tape write(2) and
      errno=0 for end of tape read(2).

    - We wrote a small C program to write(2) 5120 bytes at a time 
      to a 9-track tape on the 3B5 (using raw mode) until we got to 
      the end of tape. Then we tried to read(2) the tape (5120 bytes
      at a time) on the 3B2. To our surprise, 3B2 can read more than
      the 3B5 wrote and the 3B2 cannot detect end of tape without
      giving error warning. Reverse the read/write order, the 3B5 
      seems read less than what was put on tape by the 3B2.

So we're confused. And help is definitely needed.

Kim Tran